Two suspected terrorists have been thwarted from entering South Africa in separate incidents recently, the Hawks said on Sunday.
In the first incident, a suspected extremist, travelling on a United States passport, via Turkey, was stopped at OR Tambo on December 16.
"He was already flagged by Interpol," said Hawks spokesman Hangwani Mulaudzi said on Sunday.
"He was refused entry into the country and taken back to Turkey."
In the second incident, which also took place last month, an Iraqi man tried to fly out of Turkey to South Africa but was refused passage by Turkish authorities. He was subsequently arrested.
"They felt he held extremist views... [according to] their own intelligence."
Mulaudzi said that South African law enforcement was now awaiting an Interpol report on the matter to obtain more detail.
The Sunday Times reported that the Iraqi man was working for the Islamic State and was a bomb maker.
Iraqi ambassador Saad Kindeel was quoted in the newspaper as saying that the man "wasn't coming to South Africa to recruit for ISIS but to identify a specific target that would later be attacked".
Meanwhile, Mulaudzi told News24 said that South African officials remained vigilant and were also liaising with other law enforcement agencies to mitigate the threats of terrorism.
"South Africa is not immune from these incidents."
He said internal threats of terrorist activity also could not be dismissed.
"We are worried... but we are working around the clock to ensure that if there is any serious threat it is quelled as quickly as possible."
Most recently, in July last year, four people were arrested by officers during anti-terrorist raids carried out in Newclare‚ Florida and Azaadville in Johannesburg.
Two of those arrested were granted bail while two brothers allegedly linked to ISIS, Brandon-Lee and Tony-Lee Thulsie, both 24, remain in custody.